This invention relates to an automatic fret sawing machine and more particularly to an improved fret saw blade rotating device.
An automatic fret sawing machine has been used to cut a groove of a predetermined profile by a fret saw blade reciprocated in the vertical direction while moving a workpiece in the directions of orthogonal X and Y axes on a plane. To this end, it is necessary to conrol the fret saw blade to direct it always in the tangentional direction with respect to the profile, and the upper and lower ends of the fret saw blade are held by clamping means secured to the ends of the upper and lower driving shafts respectively which are disposed to reciprocate in the vertical direction. Since the fret saw blade is thin and delicate it is necessary to synchronously rotate the upper and lower drive shafts for rotating the saw blade about its longitudinal axis.
In a prior art driving mechanism the upper and lower drive shafts are rotated by a common drive source such as an electric motor or a hydraulic motor through various motion transmission means so that the mechanism is not only complicated and expensive but also requires troublesome maintenance. Moreover, as spaced upper and lower drive shafts are driven by a single drive source, the weight and moment of inertia of the motion transmission means are large thus making it difficult to provide a fine and accurate control. Moreover, as it is necessary to use a drive source of large power and a large number of component parts for the motion transmission means gaps between component parts make it difficult to attain accurate control.